Mobile machines, including wheel loaders, bulldozers, motor graders, and other types of heavy equipment, are used for a variety of tasks. In order to accomplish these tasks, the machines typically include a primary mover, such as an internal combustion engine that is coupled to traction devices of the machine to propel the machine. The primary mover can also be coupled to power a work implement attached to the machine.
One type of machine is known as a “high-idle” machine. During operation of a high-idle machine, an output of the primary mover is generally set to a level sufficient to quickly produce the maximum power that could be required by the traction devices and the work implement. That is, in order to ensure that the machine has power sufficient to move the machine and work implement under all conditions, the primary mover is set to a maximum output level (i.e., speed, torque, or a combination of speed and torque), even if the current task being accomplished by the machine demands less output from the primary mover. This high output level may be inefficient and result in unnecessary high fuel consumption, machine harshness, excessive exhaust emissions, and high levels of engine noise.
One way to reduce the unnecessary fuel consumption, excessive exhaust emissions, and noise associated with a high-idle machine is disclosed in U.S. Pat. No. 4,955,344 (the '344 patent) issued to Tatsumi et al. on Sep. 11, 1990. The '344 patent discloses a construction machine having an engine and a hydraulic pump utilized to power an actuator. In one embodiment, the machine includes three modes of operation: a power mode, an economy mode, and a light mode. In the power mode, corresponding to a range of operation for high-load traveling or heavy excavation, a maximum displacement of the pump is set to a smaller value and the engine is operated in a high rotational speed range. In the economy mode, corresponding to a range of operation for small-load traveling or light excavation, the maximum displacement of the pump is set to a larger value and the maximum rotational speed of the engine is limited to a speed lower than the rotational speed in the power mode. In the light mode, corresponding to a range in which the engine needs to be finely controlled, the maximum displacement of the hydraulic pump is set to the same value as in the economy mode, but the engine speed is limited to a much lower speed. This selection of the maximum displacement of the pump and the engine speed enables the construction machine to be operated by selecting the optimum engine speed and the optimum pump absorption horsepower, thereby reducing the fuel consumption rate, as well as limiting engine noise.
Although the construction machine of the '344 patent may improve fuel efficiency, emissions, and noise by offering economy and light modes of operation, it may still be suboptimal. In particular, even within the economy or light modes of operation, the machine may still be used to accomplish tasks that require less than the maximum engine output provided by that selected mode. For example, when operating in the economy mode, an unloading task requires less output from the engine than a digging task. Although the maximum available output from the engine when operating in the economy mode is less than the maximum available output from the engine when operating in the power mode, the unloading task may still require far less from the engine than is available in the economy mode. This excess available output can result in unnecessary fuel consumption, exhaust emissions, and noise. And, if the economy mode is dropped low enough such that the fuel consumption, exhaust emissions, and noise are substantially unaffected by the available output in that mode, the available output may be insufficient for some high power tasks slated for the construction machine.
The disclosed machine system is directed to overcoming one or more of the problems set forth above.